Instead of hard coding the desktop files, let's try to use what the
user actually uses.
* Browser mapped from text/html mime type
* File manager mapped from inode/directory mime type
* Email client mapped from message/rfc822 mime type
Only systemsettings is "hard coded" as there is no mime type to map.
The thumbnails are not changed, though. But they are so small that
it's hardly recognizable anyway. For future it could be considered to
map against appdata to get a better screenshot.
BUG: 310622
REVIEW: 122170
Needs to implement a dummy switcher item. As the root item of the
switchers are no longer QQuickItem derived it cannot use a QQuickView.
Instead a component gets created and the switcher is just shown on the
primary screen. It's a more appropriate preview now which is not
put into a dialog window.
To make it more realistic (and to be able to dismiss it) the preview
grabs keyboard and mouse and closes itself if escape, return, enter or
space is pressed.
As well clicking outside the preview window closes the preview.
